/Engine/Source/Runtime/Engine/Classes/Engine/InstancedStaticMesh.h
Call to flush any pending GPU data copies, if bFlushToGPUPending is false it does nothing. Should be called by the Proxy on the render thread for example in CreateRenderThreadResources().
void FlushGPUUpload ( [FRHICommandListBase](API\Runtime\RHI\FRHICommandListBase) & RHICmdList )